Overview Proteins and complexes that cannot be expressed readily in bacteria are produced in one of three different eukaryotic protein expression systems: baculovirus/insect cells, cultured mammalian cells, or in vitro translation in wheat germ extracts (in collaboration with the NIH Center for Eukaryotic Structural Genomics (CESG) at Madison, Wisconsin, John Markley, Director). As described in the main proposal, all three systems are currently being applied to produce milligram quantities of proteins and complexes of interest.